It is well known in the art to provide, at the bottom of railway cars which carry particulate materials, pairs of sloping surfaces which face each other and which are spaced apart at their lower ends for the discharge of the material between such ends. The space between the ends is blocked or unblocked by one or more manually operable valves which are opened for the discharge of the material.
It is also known in the art to provide a trough below the valves for receiving the material from which trough the material is removed through a hose or pipe connected to a vacuum system.
One successful prior art gate structure is disclosed in U.S. Pat. No. 4,500,230 and comprises a pair of downwardly converging walls separated at their lower ends. The space between the ends, in one embodiment, is occupied by two end-to-end, independently rotatable valves which have an arcuate outer surface and an inner surface which is differently shaped so that each valve increases in cross-sectional dimension from one circumferential side to a maximum intermediate cross-sectional dimension and then decreases to a smaller cross sectional dimension at the circumferentially opposite side. There is a trough below the valves for receiving the particulate material discharged past an open valve, and there is a capped discharge tube at each end of the trough to which a vacuum hose can be connected after it is uncapped, for removing the material from the trough.
Each of the valves shown in said U.S. Pat. No. 4,500,230 can be operated from only one side of the car, and the discharge tube cap is held in place by a bail. The bail retainer has been found to be unsatisfactory, and it has been found to be desirable to independently operate both valves from one side of a car. In addition, the trough structure and the attachment of the trough to the slope sheets are relatively complicated.
Said U.S. Pat. No. 4,500,230 also mentions the problem of bridging of the gap between the lower ends of the slope sheets by material being discharged or unloaded. While the gate structure of such patent has been found to be satisfactory for discharging relatively free-flowing, larger particles, bridging of the material and blocking of the discharge flow has been encountered with smaller particles such as particles of corn starch or flour. When such bridging occurs, the bridging material must be dislodged manually causing extra expense and delay in unloading a car.